1. Field of the Invention
The present invention relates in general to wind generated power and, more precisely, to airflow wind channel capture and airflow acceleration for the purpose of generating power.
2. Description of the Prior Art
It is known in the art to use turbine rotors of assorted designs and configurations for providing a rotational inertia output in response to air flow. However, prior art turbines, particularly for wind energy transformation, are limited in their effectiveness by commonly available low speed wind power transformation.
Many wind turbines are of the windmill variety wherein a multi-blade rotor is mounted so that it spins around an axis generally horizontal to the ground. The blades are exposed directly to the wind and are not housed by any means. As wind passes over and under each blade, pressure differentials cause the blades to rotate about the axis. This rotation turns gears which produces power. The amount of power or energy produced by these horizontal rotors is dependent on many factors one of the most important of which is the area swept by the rotor or, in other words, the length of the blades. Therefore, in its most common form, a tower may accommodate only a single rotor and a generator. Even the most efficient of these allows some fifty plus percent of the wind to pass through. It should be noted that some flow must be maintained through the rotor in order to produce any power at all, however, current turbines are less efficient than is desirable. The formula for power derived from the wind includes the velocity cubed. Common windmills do not accelerate the wind to take advantage of this cubing effect.
Other related art turbines attempt to capitalize on the increased velocity factor by employing a collector which includes a radius larger than the rotor at the aft end that narrows to almost equal that of the rotor. The collector captures, focuses, and accelerates more wind toward the turbine than that which would pass through a bare rotor. A turbine and collector combination may result in reducing the necessary size of the rotor. The collector allows collection of a wider range of wind directions and can greatly reduce dependence on yaw capabilities. The effects of the angle or surface curvature at which the collector's radius decreases toward the rotor on wind speed at the rotor's center or outer tips has not been well defined or studied. In addition, because a reduction of static pressure at the rotor is necessary to accelerate the wind speed passing through (and resulting power) a collector alone will not increase the power produced.
Some related art turbines are positioned in a shroud behind which a diffuser extends. The diffuser's radius increases with the distance from the rotor. As wind passes through the rotor, negative pressure will be induced at the throat with pressure recovery as it progresses to the exit. The negative pressure draws in more air through the turbine which, in turn, results in a production of more power than a bare turbine of the same size.
The amount of wind drawn through a turbine as a result of a diffuser is affected by what is known as boundary layer separation. This phenomenon occurs near the inner surface of the diffuser where wind “separates from” or does not closely follow the inner surface thereby decreasing the theoretical power increase otherwise expected. Related art has addressed this inefficiency by employing additional momentum obtained from tangential injection of the free wind around the outside of the diffuser through inlet slots in the diffuser. More than a single slot may be indicated depending on size and angle of diffuser wall relative to horizontal. By adding slots to address boundary layer separation, the angle at which a diffuser's inner surface extends can be increased and a complementary reduction in length achieved thereby reducing the length required by earlier diffuser designs.
More recent related art combines a collector, shroud, and diffuser. In addition to augmenting the power over a bare turbine, this combination shortens the time for cut-in of the turbine thus converting energy at a lower wind speed.
The traditional school of thought includes the use of massive and very long rotors for which diffusers and collectors would be both expensive and heavy. Therefore, studies have been completed to test whether the power augmentation of a given diffuser configuration would be reduced if the trailing edge of the diffuser rested on or was near the ground. These studies revealed that when the ground plane was near the trailing edge, there appeared to be an augmentation of power and that there was no decrease in power. Further studies showed the velocity across the blade plane could be improved using a bullnose on the diffuser inlet and parabolic nose cone in front of the rotor hub.
None of the related art addressed the problems heretofore suffered by large turbines. For example, tower structure expense and size. The tower must be high to support the turbine and, due to the turbine's weight, the structure must be equally substantial as well as equipped to function against wind shear.
In addition, related art mostly employ single rotors that generate no power if the rotor fails. Finally, although efforts have been made to augment the power of a turbine, no efforts seem to have been made to actually use more of the wind mass passing the rotor blades.
More recently, related art has considered using a multiple of modules housing small rotors stacked vertically. These arrangements require less land area and provide redundancy such that the malfunction of one rotor does not shut down power generation. Specifically, this arrangement employs toroidal accelerator rotor platform systems which function by placing an obstruction in the path of the wind which causes the air to accelerate around it. A rotor is then placed in the region of highest local velocity. Using multiple such rotors substantially increases the system power output over rotors in free stream. The system uses the inner part of a toroid with a pair of rotors mounted in the semi-circular channel separated by 180 degrees so that both face the wind. Toroidal modules are then stacked upon one another. The rotors are free to yaw within the channel to face the wind.
The present invention differs from the above referenced inventions and others similar in that these prior devices typically employ one turbine per tower and depend on very large rotor swept areas. Although strides have been made to augment wind power using collectors and diffusers, even the modular types employing smaller rotors still allow over half of the wind (and its power) to pass through rotors unhindered and unharnessed.
One object of the present invention is to greatly enhance the power produced by a single tower by augmenting the power of each turbine and by utilizing more of the wind passing through the rotors;
A second object of the present invention is to provide a device that uses air channels to amplify airflow through the rotor along with associated collectors and diffusers;
A third object of the present invention is to provide a device wherein multiple rotors may be associated with one another to enhance efficiency;
A fourth object of the present invention is to reduce tower structure needs;
A fifth object of the present invention is to provide selective pitch control for rotors;
A sixth object of the present invention is to effectively capture and use wind power from any direction;
A seventh objective is to reduce the costs associated with wind power production by increasing the power produced per tower erected. This reduces land use and greatly increases the ratio of electricity generated to erected tower cost; and
An eighth objection is to provide a wind power generative device that is more avian friendly by providing physical profiles detectable by birds and bats.